Filtering method for the detection of the transitions of a power steering signal

Abstract

The invention concerns a method for detecting a transition (4′) in a noisy signal, which involves submitting a noisy signal (δSignal) carrying an item of information used for managing the power steering, said method comprising a derivation sub-step (a1), which involves evaluating the time derivative of the noisy signal (δSignal/δt), following by a selective filtering sub-step (a2) which involves comparing said time derivative of the noisy signal (δSignal/δt) with a predefined variation threshold (Spic) in order to detect the appearance of a derivative peak (7), greater than said variation threshold (Spic), evaluating the holding time (dpic) of said derivative peak, during which the time derivative of the noisy signal (δSignal/δt) is held above said variation threshold (Spic), and checking if said peak holding time (Spic) reaches or exceeds a predefined minimum time threshold (d0).

The invention claimed is: 
     
       1. A power steering management method comprising:
 obtaining a noisy signal from at least one sensor configured to measure a motor torque or a torque exerted by a driver on a steering wheel in a power steering system; and 
 detecting transitions in the noisy signal, the noisy signal including information used for assisting a driver in maneuvering a power steering of the power steering system, 
 wherein the detecting of a transition comprises:
 determining a time derivative of the noisy signal; and 
 filtering the noisy signal to detect the transition, so as to generate a filtered signal including the information used for assisting the driver in maneuvering the power steering, and to exclude noise from the noisy signal, 
 
 wherein the filtering comprises:
 comparing the time derivative of the noisy signal to a predetermined variation threshold in order to detect the appearance of a derivative peak greater than the variation threshold, the derivate peak being an indication of a reversal of a steering direction; 
 determining a holding duration of the derivative peak, during which the time derivative of the noisy signal is held above the variation threshold; and 
 determining whether the holding duration of the derivative peak is greater than or equal to a predetermined minimum duration threshold, so as to isolate the derivative peak of the transition to be detected from derivative peaks of the noise, which have a holding duration lower than the holding duration of the derivative peak of the transition to be detected, 
 
 wherein the minimum duration threshold is selected to be greater than or equal to a maximum half-period characteristic of noise that affects the noisy signal, and less than a duration characteristic of the transition to be detected, and 
 wherein a motor of the power steering system outputs an assistance force, which is based on the filtered noisy signal, so as to assist the driver in maneuvering the power steering. 
 
     
     
       2. The method according to  claim 1 , wherein the minimum duration threshold is between 30 ms and 40 ms. 
     
     
       3. The method according to  claim 2 , further comprising:
 after detecting the transition, characterizing the transition by identifying a peak start instant, which corresponds to an instant at which the time derivative of the noisy signal passes above the variation threshold, and identifying a peak end instant, which corresponds to an instant at which the time derivative of the noisy signal again descends below the variation threshold. 
 
     
     
       4. The method according to  claim 3 , wherein at least one of the variation threshold and the peak holding minimum duration threshold is adjusted based on an angular acceleration of the steering wheel. 
     
     
       5. The method according to  claim 2 , wherein at least one of the variation threshold and the peak holding minimum duration threshold is adjusted based on an angular acceleration of the steering wheel. 
     
     
       6. The method according to  claim 1 , further comprising:
 after detecting the transition, characterizing the transition by identifying a peak start instant, which corresponds to an instant at which the time derivative of the noisy signal passes above the variation threshold, and identifying a peak end instant, which corresponds to an instant at which the time derivative of the noisy signal again descends below the variation threshold. 
 
     
     
       7. The method according to  claim 6 , wherein at least one of the variation threshold and the peak holding minimum duration threshold is adjusted based on an angular acceleration of the steering wheel. 
     
     
       8. The method according to  claim 1 , wherein at least one of the variation threshold and the peak holding minimum duration threshold is adjusted based on an angular acceleration of the steering wheel. 
     
     
       9. A power steering system comprising:
 a motor; and 
 a processor programmed to:
 obtain a noisy signal from at least one sensor configured to measure a motor torque or a torque exerted by a driver on a steering wheel in a power steering system; and 
 detect transitions in the noisy signal, the noisy signal including information used for assisting a driver in maneuvering a power steering of the power steering system, 
 
 wherein detection of a transition comprises:
 determining a time derivative of the noisy signal; and 
 filtering the noisy signal to detect the transition, so as to generate a filtered signal including the information used for assisting the driver in maneuvering the power steering, and to exclude noise from the noisy signal, 
 
 wherein the filtering comprises:
 comparing the time derivative of the noisy signal to a predetermined variation threshold in order to detect the appearance of a derivative peak greater than the variation threshold, the derivate peak being an indication of a reversal of a steering direction; 
 determining a holding duration of the derivative peak, during which the time derivative of the noisy signal is held above the variation threshold; and 
 determining whether the holding duration of the derivative peak is greater than or equal to a predetermined minimum duration threshold, so as to isolate the derivative peak of the transition to be detected from derivative peaks of the noise, which have a holding duration lower than the holding duration of the derivative peak of the transition to be detected, 
 
 wherein the minimum duration threshold is selected to be greater than or equal to a maximum half-period characteristic of noise that affects the noisy signal, and less than a duration characteristic of the transition to be detected, and 
 wherein the motor outputs an assistance force, which is based on the filtered noisy signal, so as to assist the driver in maneuvering the power steering. 
 
     
     
       10. The filter according to  claim 9 , wherein the minimum duration threshold is between 30 ms and 40 ms.